Method and apparatus for mixing and spreading road material



April 3, 1934. T w. ALLEN ET AL 1,953,890

G ROAD MATERIAL METHOD AND APPARATUS FOR MIXING AND SPREADIN Filed July 5, 1 932 5 Fig.4

Patented Ap 3, 1934 UNITED STATES PATENT OFFICE .METHOD AND APPARATUS FOR MIXING AND SPREADING ROAD MATERIAL T Warren Allen and Clarence F. Rogers,

Washington, D. C.

(Granted under the act of March 3, 1883, as amendedAprll 30, 1928; 370 0. G. 757) This application is made under the act of March 13, 1883, chapter 143, as amended by the act of April 30, 1928, and the invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes without payment to the applicants of any royalty thereon.

This invention relates to improvements in the equipment for and method of constructing road surfaces and has for its object to expedite the mixing process and to render it considerably cheaper. This invention is an application of the principle of the twin-shaft pugmill mixer, commonly used on stationary asphalt plants, to a machine for and a method of continuous mixing of all the material comprising the roadway surface, while travelling longitudinally along and mixing directly upon the roadway subgrade.

' Whereas other methods require the use of a considerable number of machines making numerous, successive passes through the material being mixed, our method combines the functions of mixing in a single machine, making a'single passage through the material being mixed.

5 Whereas other methods, combining the functions of mixing in a single machine, require the elevation of the surfacing material, ainst the forces of gravity, by means of mechanical appurtenances other than the mixer itself, our 0 method permits all necessary elevation of the material, against the forces of gravity, to be accomplished by, and to any desired elevation within, the mixer itself.

Whereas other single-unit machines employ a 5 single rotating, shaft in a confined space, our

machine employs twin-shafts, operating transversely across the roadway and rotating in opposite directions.

Whereas other machines employ paddles set 40 on extended arms fixed or fastened to a rotating shaft to accomplish mixing by means of the principle of the discontinuous screw, our machine employs twin-shafts, through which extend paddle arms, on which are fixed or fastened paddles, 5 the alignment, spacing and thrust of which, ac-

complishes the violent agitation requisite to proper mixing, of allthe material within the mixer enclosure above the plane surface of the subgrade, in a single passage of the machine.

Whereas the paddles of other rotating shaft mixers are flat-nosed and of uniform width, the paddles of our mixer are bevelled to angular sharpness and widened at the nose, to expedite the clean sweeping of the material from the plane 65 surface of the subgrade and to prevent the impediment to mixing presented by the bridging of material between the paddle ends and the lower horizontal plane of mixing action.

Whereas other methods and other road mixing machines permit the mixing of material in amounts such as are encountered longitudinally along the roadway, our mixer acts as a reservoir and actually accomplishes the longitudinal drifting of material, thus rectifying unequal, longitudinal distribution and contributing to a highly desirable uniformity in the cross-section of the road surface being mixed.

The preferred form of the invention is illustrated in the accompanying drawing in which:

Figure l'is a side elevation of the entire machine, composed of a mixer. supported between crawler tracks connected by two main frames.

Figure 2' is a side elevation of the machine as it appears after the crawler tracks and main connecting frames have been removed.

Figure 3 is a side elevation of the mixer after removal of the bed plates and side of mixer, showing adjustable gates, and operating mechanism to control opening, in position to admit and dise charge the road surfacing material being mixed.

Figure 4 is a plan view of the entire machine showing main frame connection to front and rear bed plates, with the entire mixer enclosure exposed. Y

Similar numerals refer to similar parts throughout the several views. Referring to the drawing, the operation of this machine and the method by which it readily converts unmixed roadway surfacing material and binder or matrix into a completely mixed and a uniformly distributed prod-I uct, may be observed. In this connection, it is desired to point out that, with the approaching com- 7 pletion of the primary system of highways in the United States, there still remains a vast mileage of secondary highways to be surfaced. So great is this mileage of feeder routes and farm-tomarket roads that no conception of ultimate completion may be entertained except by the employment of a strictly low-cost surfacing. Such a condition demands the elimination of the highdegree of refinement typical of the road surfacing used on the primary system. In order that cheap, roadside and local aggregates may be employed, the requirements as to gradation must be sacrificed to the use of pit-run or crusher-run materiah To further lower the cost of production, the use of multiple aggregates of several graded sizes must be dispensed with in favor of a single size dependent upon local conditions. Economy further demands that roads constructed of such material be bound with a comparatively cheap matrix. The road oil mix of the western United States and the macadams grouted with lean cement mortar as well asto the lean cement mixes are typical of such types as are commensurate with low cost. The oil mix road, designated mixed-in-place, has been widely constructed without undue refinement, under varied conditions of aggregate, binder and climate. The chief criterion of its successful use lies in the complete and thorough mixing and the uniform distribution of the aggregate with the binding media. Tractor-drawn blades have been widely used for mixing. The dry surfacing material is first scarified to a uniform subgrade or base and loosened, after which the binding medium, in this case a low grade asphaltic fuel oil, is added to the material on the road. The material is then bladed into and out of windrows and layers, transversely across the roadway, repeatedly until thoroughly mixed. Generally, several tractor and blade combinations are used, the cost of which can be considerably reduced by the use of a single-unit machine accomplishing the same mixing task inv a single passage through the material. Our invention is such a machine designed to mix the several ingredients of the road surface whether the binding media is added to the material on the roadway or sprayed continually into the mixer enclosure as the machine progresses along the roadway.

The complete machine may be pulled or towed along the road by means of a standard independent tractor or may be driven under its own power by means of a standard engine or motor 1, with worm drive 2, through standard, two-speed forward and reverse, transmission box 3, thence'by chain drive through separate standard clutches activating chain drives to standard rear crawlers 4 and 5. In either case, the entire machine moves continually forward, longitudinally along the roadway during the mixing. In all cases, the mixer is driven at constant speed from engine work drive 2 to conventional throwout clutch box 6, thence to standard drive sprocket with chain drive 7, to rear mixer shaft 8, connected on the opposite side of the mixer by equal and opposite change gears 9 and 10, to cause equal and opposite rotation, at high speed, of the two main shafts of the mixer with upward rotation at the center.

Whether the binding media is added to the surfacing material on the roadway or sprayed in at the mixer, the aggregate ahead of the mixer is bladed into a windrow such as will pass between the mixer sides or within a transverse distance of eight feet or less. Material enters the mixer through front gate 12. This gate is adjustable to control the size of the opening above the subgrade on which the machine operates, to strike off and spread the windrow to the width of the mixer. A handwheel 13 controls the elevation of the gate through a reduction gear and rack, enabling facile operation, convenient to adjust from the platform of bedplate 35. A brake ratchet 14 is provided to lock the gate in a fixed position.

The ingredients of the road surface, within the mixer, depend for thorough mixing upon the violent agitation imparted by the forty-eight paddles on the twenty-four paddle arms set through the two rotating shafts. Figure 4'also shows the paddles 36, paddle arms 37 and shafts 8 or 11, showing the manner in which the paddle arms are aflixed to the mixer shafts; the manner in which the paddles are aflixed to the paddle arms; the

manner in which the paddles are placed at an angle of 45 degrees with the plane of rotation to thrust the material transversely across the mixer, and the arrangement of the paddles which, with the spacing along the shaft and the frontal width of the paddle enables the complete closure across the mixer so that all the material enteringthe mixer is struck and loosened and swept ahead of the force of the moving, paddles at the subgrade. Since all the material may be mixed longer, the rear gate, identical with gate '12, is closed to permit material to accumulate within the mixer. When the mixer is nearly filled, the rear gate is opened to discharge 'an amount of material, in a uniform cross section, equivalent to the average amount entering the front gate, the mixer acting as a reservoir to compensate for inequalities of supply in. the windrow ahead of the mixer. This feature permits the machine to leave a more uniform cross section of mixed material than generally exists in the unmixed windrow and results in a finished surface of more uniform depth, a highly desirable condition.

Complete mixing depends upon all the loose material being violently agitated. To enablev keeping the mixer at the proper elevation so that the paddles will strike just above the subgrade or base of the roadway, a mechanical device to raise or lower the mixer with respect to the elevation of the subgrade, is provided, together with a lever arrangement designed to keep the mixer at a constant elevation with reference to that of the crawler tracks. Handwheel 15 activates worm and gear 16, driving shaft 17, and through bevel gears 18 and 19 to drive equal and opposite thread screws. Both sides of the front connection are identical. Screw 20 is fixed in jacket 21, rigidly anchored to the mixer. Screw 20 engages bracket arm 22, housed and sliding in jacket 21. Since bracket arm 22 is fixed to rigid lever arrangement, to lever 23 slung on pins between lever 24 to frame and lever 25 to rear axle 26 of the front crawler track, the movement of handwheel 15 results in the movement of the mixer about the connecting bracket to the lever arrangement.

Handwheel 27 activates a similar arrangement, raising or lowering the mixer at the rear, except that bracket arm 28 is a unit with axle 28 of the front tumbler sprocket of the rear crawler track. Thus, for a set position on the lift screws, the rear of the mixer moves with. the front end of the crawler track through the direct connection while the front of the mixer moves with the rear end of the front crawler track, through the indirect action of the levers 23, 24 and 25.

To permit of shop assembly of the paddles, arms and shafts, which may then be set in place in the mixer, slip housings 29, 30, 31 and 32 are used. These are accompanied by follow-up plates 33 and 34, to close the openings in the mixer through which the shaft assemblies are inserted. These slip housings further enable or permit the shafts to raise in the mixer, thus allowing the paddles to clear possible obstructions in the surfacing material or on the base or subgrade.

Mixing is accomplished by violent agitation of turning and displacing of all ing is shown in Figure 4. On shaft 11 the sixteen paddles 36 on the eight arms 37 on one end of the shaft are set to thrust the material toward the opposite end, of the shaft, past the transverse center of the mixer. The other eight paddles on the four remaining arms of shaft 11 are faced to thrust the material in the opposite direction. On shaft 8, the exact end-about setting of paddles is preferred. This paddle setting combination has been derived to best accomplish the function of proper mixing and complete distribution by means of experiments conducted with a motordriven, wheel model of this machine. The model was constructed of steel to one-sixth the linear measure of the large size machine and its operation substantiates the contentions and claims of the modus operandi herein discussed.

We claim:

1. A road surface mixing machine, of the character described, comprising a suitable frame provided with ground engaging supports; a mixing compartment supported by said frame and said supports; a front gate slidably mounted on the forward upright wall of said mixing compartment; agitating means within said mixing compartment for mixing surfacing material without removing the mass from the road grade; means for imparting motion to said agitating means; and a rear gate slidably mounted on the rear upright wall of said mixing compartment.

2. A road surface mixing machine, of the character described, comprising a frame provided with ground engaging supports; means for propelling said mixing machine upon said support; a mixing compartment comprising upright joined walls supported by said frame and said supports; means for adjusting the elevation of said mixing compartment substantially to the elevation of the rear ends of the forward ground engaging supports and the front ends of the rear ground engaging supports while in motion; means for adjusting the elevation of the forward end, and means for adjusting the elevation of the rear end of said mixing compartment; a front gate slidably mounted on the forward upright wall of said mixing compartment; means for raising and lowering said front gate to regulate the rate of passage, into said mixing compartment, of unmixed surfacing material, reposing on the road grade, as the machine progresses longitudinally along the roadway; means for mixing surfacing material within said mixing compartment without removing the mass from the road grade; a rear gate slidably mounted on the rear upright wall of said mixing compartment; means for raising or lowering said rear gate to regulate the rate of passage, from said mixing compartment, of the mixed material, uniformly spread by said rear gate, as the machine progresses longitudinally along a roadway; means for setting said front gate, and means for setting said rear gate in a fixed position; cooperative means for depressing said rear gate, and elevating said front gate, thus causing said material to accumulate within said mixing compartment, while the machine is in motion; and cooperative means for depressing said front gate, and elevating said rear gate, thus causing said material to unaccumulate within said mixing compartment, while the machine is in motion.

3. A method of road surface construction, which comprises accumulating at a non-uniform rate surfacing material from a prepared windrow; thence simultaneously adding a binding media to said accumulated material, and thoroughly mixing the combined ingredients, and spreading at a uniform rate the resulting mixture; continuing and progressing said action along a roadway, without substantially removing the mass of said material therefrom.

4. A method for surface construction, which comprises loosening surfacing material, adding a binding media and preparing a windrow therewith; thence accumulating at a non-uniform rate the ingredients of said windrow and thoroughly mixing the combined ingredients without substantially removing the mass of said ingredients from the surface, and spreading at a uniform rate theresulting mixture.

5. A method for road surface construction, which comprises initially preparing surfacing material in a windrow along a roadway; thence continuously causing said material to be confined, accumulated substantially in reserve, forwardly conveyed and subjected to violent agitation and applying a binding media thereto, and thoroughly mixing, longitudinally distributing and uniformly spreading the resulting mixture on the road grade, the mass of said material substantially remaining thereon.

6. A method for road surface construction, which comprises initially preparing surfacing material in a windrow along a roadway; thence continuously causing said material to be confined,

, accumulated substantially in reserve, rearwardly conveyed and subjected to violent agitation and applying a binding media thereto, and thoroughly mixing, longitudinally distributing and. uniformly spreading the resulting mixture on the road grade, the mass of said material remaining substantially thereon. 

